Combined drive for a four-or-six-high rolling stand and an operating method for the same

ABSTRACT

The invention relates to a four- or six-high rolling stand for a rolling train and to a method for operating the same. The aim of the invention is to provide rolling stands that can adapt rapidly to rolling products of different thicknesses and/or hardnesses. To achieve this, rolling stands are provided with minimum expenditure that can be selectively operated with both thin and thick working rolls. The inventive combined drive in the four- or six-high rolling stand allows thick working rolls to be directly connected to a motor, whereas thin working rolls are merely carried along by neighbouring back-up rolls or intermediate rolls by means of friction.

[0001] The invention relates to a four-high roll stand according to the introductory clause of claim 1 and a six-high roll stand according to the introductory clause of claim 2 as well as to a method of selectively driving the four- or six-high roll stands with small- and large-diameter working rolls.

[0002] A rolling string has one or more roll stands. The roll stands grip the workpiece strip with working rolls that are rotated oppositely to each other in the rolling direction. This rotation of the working rolls advances the workpiece. The height of the rolling nip determines the thickness to which the working rolls reduce the workpiece. A four-high roll frame (quarto) has two working rolls and two backing rolls. A six-high roll frame (sexto) has two working rolls, two outer backing rolls, and, between each outer backing roll and the respective working roll, an inner backing roll.

[0003] In order to roll very thin strip in a rolling string (hot or cold) small-diameter working rolls are used in the furthest downstream roll stand. They reduce the rolling force, the edge drop, and the temperature loss of the workpiece and also normally spare the roll stands of the rolling string because greater thickness reductions can be achieved.

[0004] Normally it is desirable to be able to hot roll not only very thin strip, but a thickness range from for example 0.8 mm to 12.7 mm. As a result of this requirement with respect to productivity, optimizing the roll string for thin strip is not possible for the following reasons:

[0005] Optimizing requires that for example the furthest two downstream roll stands with small-diameter working rolls be driven. The drive stubs and shafts of these small-diameter working rolls are often overloaded when rolling thick and/or hard strip. Switching out the small-diameter working rolls for large-diameter ones requires the drive shafts to be changed. The resultant down time of the rolling string is not acceptable.

[0006] German patent document 3,411,853 describes a four- or six-high roll stand with driven backing rolls where the working rolls are driven frictionally by the backing rolls. In order to modify the operational characteristics of the rolling stand when it is driven at only a fraction of its capacity and such that the drive can be controlled accurately and loaded efficiently, it has been suggested that one of the drive motors be connected via a transmission with its backing roll and be uncoupled from this backing roll and shut down so that the load of the remaining drive motor is doubled and it can be controlled within the standard range more accurately.

[0007] The working rolls themselves have no drives but are in all case connected together by a synchronizing transmission so as to avoid any slip of the working rolls. Switching this type of rolling stand to large-diameter working rolls is neither foreseen nor possible, since it is impossible to drive the working rolls frictionally with a thicker strip exclusively from the backing rolls.

[0008] Based on this state of the art, it is an object of the present invention to provide a rolling stand that permits a quick adaptation to strips of different thicknesses and/or hardnesses.

[0009] In order to simply be able to operate with small-diameter and large-diameter working rolls in the same stand, in a four-high stand according to the invention the other backing roll is also connected via a releasable connection with a motor and the two working rolls are each connectable via a releasable connection with the motor.

[0010] For a six-high rolling stand the outer backing rolls, inner backing rolls, and working rolls are driven by a motor through respective drive shafts that are each provided with a releasable connection.

[0011] This combined drive in a four- or six-high roll stand according to the invention makes it possible to couple large-diameter working rolls via the respective releasable connections directly with a motor while when small-diameter working rolls are used in a four-high roll stand the drive is effected via the two backing rolls which in this case are connected via releasable connections with the motor. The small-diameter working rolls are thus only driven by friction from the backing rolls. Similarly in a six-high roll stand in order to drive small-diameter working rolls only the outer backing rolls and/or the inner backing rolls are connected via the respective releasable connections with the motor while to drive large-diameter working rolls, these working rolls are themselves connected via the respective releasable connections with a motor.

[0012] According to the invention there is only a connection between a roll and the motor when torque is transmitted from the motor via, if necessary, an intermediate transmission and the releasable connection to the drive shaft. No connection to the motor as here defined is provided for the roll when it is driven by friction from another driven roll.

[0013] The releasable connections for connecting the working rolls with the motor are formed as clutches which can be of the mechanical, electrical, hydraulic, or pneumatic type.

[0014] The roll stand can be constructed such that the releasable connections for the drive stubs of the working rolls are couplings that can be fitted to and pulled off the drive shafts. To this end the drive shafts can telescope to accommodate this type of connection. Finally it is advantageous and particularly interesting from a manufacturing point of view according to the invention when the small-diameter working rolls have no drive stubs so that the coupling on their drive spindles are ineffective. Thus in this case the coupling for the small-diameter working roll is separated from the drive shaft. The drive shafts for the working rolls thus run free.

[0015] Uniform and cost-effective driving of all the rolls is achieved when the two working rolls are connected to the working-roll motor via a transmission, in particular a continuous-mesh transmission. Alternately it is also possible when only the two working rolls are connected to a common working-roll drive motor via a transmission, in a particular a continuous-mesh transmission, while the backing rolls are provided with separate upper and lower drive motors.

[0016] The spacing between the backing rolls or the inner backing rolls is dependent on the diameter of the working rolls being used can be compensated for by appropriate adjustment devices, as for example stepped wedges at the upper and lower ends of the roll-stand frame.

[0017] Preferable methods of operating the roll stand according to the invention with small- and large-diameter working rolls as well as working-roll combinations of different diameters are seen in the features of claim 8 to 11.

[0018] Preferably the roll stands according to the invention use small-diameter working rolls with a low-friction coating, in particularly metallurgical powder (high-strength HSS rolls). These working rolls can be made by the HIP (hot isostatic pressing) technique.

[0019] In the following the invention is described more closely with reference to a four-high roll stand.

[0020] Therein:

[0021]FIG. 1 is a four-high roll stand working with small-diameter working rolls; and

[0022]FIG. 2 is a four-high roll stand working with large-diameter working rolls.

[0023]FIG. 1 shows schematically backing rolls 1 and 2 of a four-high roll stand between which are small-diameter working rolls 4 and 5 for strip 3 of limited thickness.

[0024] In order to drive the rolls 1, 2, 4, and 6 there is a continuous-mesh transmission 6 driven by a drive motor 7. The continuous-mesh transmission 6 is comprised of two central working-roll gears 8 and 9 and upper and lower backing-roll gears 11 and 12.

[0025] The backing rolls 1 and 2 as well as the working rolls 4 and 5 have drive shafts 13, 14, 15, and 16 that are connected through the continuous-mesh transmission 6 with the motor 7. The drive shafts 13 and 16 for the backing rolls 1 and 2 have respective clutches 17 and 18 that can be opened to interrupt the transmission of torque between the motor 7 and the backing rolls 1 and 2.

[0026] In order to drive the small-diameter working rolls 4 and shown in FIG. 1, the clutches 17 and 18 are closed in order to drive only the backing rolls 1 and 2, letting the working rolls 4 and 5 and their shafts 14 and 15 rotate freely. In the illustrated embodiment the apparatus with the small-diameter working rolls 4 and 5 has couplings 19 and 21 that are provided on the shafts 14 and 15 of the continuous-mesh transmission 6 and that serve to connect to drive stubs of large-diameter working rolls. Since the working rolls 4 and 5 of FIG. 1 have no drive stubs, there is no force transmission from the motor 7 to the working rolls 4 and 5.

[0027] If working conditions require, as shown in FIG. 2, large-diameter working rolls 24 and 25 can be used with no difficulty in the four-high roll stand according to the invention. The four-high stand of FIG. 2 is different from that of FIG. 1 in that the two backing rolls 1 and 2 are connected directly via their drive shafts 13 and 16 with separate respective backing-roll motors 26 and 27. This difference is however irrelevant to operation here.

[0028] The large-diameter working rolls 24 and 25 have drive stubs 28 and 29 that are connected to the couplings 19 and 21 of the drive shafts 14 and 15. Torque is transmitted to the large-diameter working rolls 24 and 25 via the spindles 14 and 15 and the continuous-mesh transmission 6 from the motor 7 which in this embodiment only drives the working rolls 24 and 25.

[0029] The clutches 17 and 18 for the drive shafts 13 and 16 of the backing rolls 1 and 2 are open so that the backing rolls 1 and 2 idle and the backing-roll motors 26 and 27 can be shut off.

[0030] Of course it is also possible with the four-high stand according to FIG. 1 and FIG. 2 to provide clutches for the drive shafts 14 and 15 in order to interrupt torque transmission from the motor to the working rolls when small-diameter working rolls are being used.

[0031] In order to conform the spacing between the backing rolls 1 and 2 with the diameters of the workings 4 and 5 or 24 and 25, stepped wedges not illustrated in the drawing are provided on the upper and lower ends of the roll stand. All the drive shafts are formed as is known as cardan shafts in order to compensate for any offset between the axes of the driving and driven parts.

[0032] Thus the invention allows fast changing of rolling stock with respect to thickness and/or hardness in that the roll stand can be easily setup to work with both small- and large-diameter working rolls. The combined drive according to the invention in four- and six-high roll stands make it possible to connect large-diameter working rolls directly with a motor while small-diameter working rolls are driven only by friction from the adjacent backing rolls.

[0033] Parts List Number Identification  1 Backing roll  2 Backing roll  3 Thin rolling strip  4 Working roll  5 Working roll  6 Continuous-mesh transmission  7 Motor  8 Working-roll drive gear  9 Working-roll drive gear 10 11 Backing-roll drive gear 12 Backing-roll drive gear 13 Drive shaft 14 Drive shaft 15 Drive shaft 16 Drive shaft 17 Clutch 18 Clutch 19 Coupling 20 21 Coupling 22 Drive stub 23 Drive stub 24 Large-diameter working roll 25 Large-diameter working roll 26 Motor 27 Motor 28 Drive stub 29 Drive stub 

1. A four-high rolling stand with two working rolls and two backing rolls driven via drive shafts, one of the backing rolls being connected via a releasable connection with a motor, characterized in that the other backing roll (2) is also connected via a releasable connection (16) with a motor (7) and the two working rolls (4 and 6) are each connected via a releasable connection (19 or 21) with the motor (7).
 2. A six-high rolling stand with two working rolls, two outer backing rolls, and two inner backing rolls between the outer backing rolls and the working rolls, characterized in that the outer backing rolls, inner backing rolls, and working rolls are driven by a motor through respective drive shafts that are each provided with a releasable connection.
 3. A roll stand according to claim 1 or 2, characterized in that the releasable connection for connecting the backing and/or inner and/or outer backing rolls with the motor (7) or motors (26 and 27) are formed as clutches (17 and 18).
 4. The roll stand according to one of claims 1 to 3, characterized in that the releasable connections for the drive stubs (28 and 29) of the working rolls (4 and 5) are couplings (19 and 21) on the drive shafts (14 and 15).
 5. The roll stand according to one of claims 1 to 4, characterized in that the working rolls (4 and 5) have no drive stubs.
 6. The roll stand according to one of claims 1 to 5, characterized in that the two working rolls (24 and 25) are connected to the working-roll motor (7) via a transmission (6), in particular a continuous-mesh transmission.
 7. The roll stand according to one of claims 1 to 6, characterized in that the backing and working rolls are connected to a common motor (7) via a transmission (6), in particular a continuous-mesh transmission.
 8. A method of driving a four-high roll stand cc claim 1 with first small-diameter working rolls and second large-diameter working rolls, characterized in that in order to drive the small-diameter working rolls (4 and 5) only the backing rolls (1 and 2) are driven and to drive the large-diameter working rolls (24 and 25) only the working rolls (24 and 25) are driven from a motor (7 or 26, 27).
 9. A method of simultaneously driving a first small-diameter working roll and a second large-diameter working roll in a four-high roll stand according to claim 1, characterized in that in order to drive the small-diameter working roll only the respective backing roll (1 or 2) is driven and the large-diameter working roll is directly driven by a motor (7, 26, or 27).
 10. A method of selectively driving a six-high roll stand according to claim 2 having first small-diameter working rolls and second large-diameter working rolls, characterized in that in order to drive the small-diameter working rolls only the outer backing rolls and/or the inner backing rolls are driven and the large-diameter working rolls are directly driven by a motor.
 11. A method simultaneously driving a first small-diameter working roll and a second large-diameter working roll in a six-high stand according to claim 2, characterized in that in order to drive the small-diameter working roll only the respective outer and/or inner backing roll is driven and the large-diameter working roll is driven directly by a motor.
 12. The method according to one of claims 8 to 11, characterized in that the small-diameter working roll has a surface made of a low-friction material, in particular a powder-deposited metal. 